I didn't see in this thread where you mentioned water quality tests..
Poor water quality will stress the fish and make them susceptible to infection and disease.
There should be somewhere on the Island that can sell you some water test kits.
These are the ones that are most popular:
https://www.apifishcare.com/product.php?id=580#.W__t3mhKhhE
https://www.apifishcare.com/product.php?id=587#.W__t-GhKhhE
Once we know your water quality based on the above test kits (get both), we can help you improve your water quality and treat from there.
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Thanx i will buy the test tomorrow